The present invention relates to an imaging lens for forming an image on an imaging element such as a CCD sensor and a CMOS sensor. In particular, the present invention relates to an imaging lens suitable for mounting in a relatively small camera such as a cellular phone, a digital still camera, a portable information terminal, a security camera, an onboard camera, and a network camera.
An imaging lens for mounting in a small-sized camera requires a lens configuration with high resolution that can be suitably applied in an imaging element of high resolution that is available in these years, in addition to having a small size. Conventionally, there have been various proposals for lens configurations, and among them, an imaging lens with a three-lens configuration has been used in many cameras since such an imaging lens can relatively satisfactorily correct aberrations and is suitable for miniaturization.
For such an imaging lens with a three-lens configuration, for example, an imaging lens described in Patent Reference has been known. The imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; and a third lens having positive refractive power, arranged in the order from an object side. According to the configuration, the third lens has shorter focal length than that of the whole lens system, i.e., the third lens has relatively strong refractive power. At the same time, the second lens has stronger refractive power than that of the first lens so as to correct field curvature, coma aberration, and so on.    Patent Reference Japanese Patent Application Publication No. 2008-76594
In recent years, there have been rapid advancements in miniaturization and higher resolution of cameras as well as cellular phones, and demands for performances of imaging lenses have been even higher than before. According to the conventional imaging lens described in Patent Reference, it is possible to relatively satisfactorily correct aberrations. Since the whole lens system has a long focal length, however, the length of the imaging lens on an optical axis tends to be long, and there is limitation in miniaturization of the imaging lens.
Here, such a requirement of attaining both miniaturization and aberration correction is not a challenge specific to the imaging lens for mounting in a cellular phone, but also a challenge for an imaging lens for mounting in a relatively small camera, such as digital still cameras, portable information terminals, security cameras, onboard cameras, and network cameras.
In view of the above-described problems in the conventional techniques, an object of the present invention is to provide an imaging lens that can satisfactorily correct aberrations despite of a small size thereof.
Further objects and advantages of the invention will be apparent from the following description of the invention.